The present invention relates generally to electrical machines commonly known as alternators. More specifically, the present invention relates to an improved alternator in which an exciting or field current is supplied to a rotor assembly so that the rotor assembly and a stator assembly may electromagnetically cooperate to generate an AC current for use by and in the operation of, for example, motor vehicles such as heavy duty and business class trucks.
The basic function of an alternator is to generate the AC current. Two types of alternators, a brush-type alternator and a brushless-type alternator, have been commonly employed by the art.
In brush-type alternators, the exciting (DC) current is conventionally supplied to the rotor assembly, in part, by brushes that are in physical, sliding contact with a portion of the rotor shaft of the alternator. Brushless-type alternators, as the name implies, do not use brushes in supplying the exciting current. Rather the exciting current is supplied to the fixed core or stator so that there is a stationary field.
The employment of brushes is a long recognized disadvantage for brush-type alternators. The brushes tend to wear, due to the xe2x80x9cmechanical,xe2x80x9d brush-to-rotor shaft contact, and have a relatively short life as compared to the rest of the alternator components. Worn brushes must be replaced, and such replacement can be time consuming and expensive.
Further, the brushes used in brush-type alternators can produce sparks that may damage other nearby equipment, or may create electromagnetic interference problems. Brush-type alternators also tend to be noisy and are sensitive to dusty environments.
Brushless-type alternators overcome the brush related problems associated with brush-type alternators. However, compared to equivalent brush-type alternators, present brushless-type alternators are inefficient in terms of AC current output. They tend to be much larger in size and heavier than comparable output brush-type alternators. Brushless-type alternators are also more expensive than comparable output brush-type alternators.
Accordingly, a primary object of the present invention is to provide an improved alternator that overcomes the problems related to the brush-type alternators and disadvantages of the brush-type alternators while avoiding the weight, size, cost and electrical output disadvantages inherent in present brushless-type alternators.
Another object of the present invention is to provide an improved alternator in which the exciting current is supplied to the rotor assembly, as in a conventional brushtype alternator, but without employment of the conventional brushes or other structure that results in relatively high friction, high wear due to mechanical contact between a rotating member and a relatively fixed member.
A further object of the present invention is to provide an improved alternator having a rotor assembly, which includes a rotatable shaft that rotates, as the rotor assembly rotates, about the shaft""s longitudinal axis; a stator assembly that electromagnetically cooperates with the rotating rotor assembly so an AC current is generated upon the supply of an exciting current to the rotor assembly; and an improved contact assembly including: at least one, first, relatively fixed member that is disposed adjacent to the rotatable shaft and that is electrically conductive to the exciting current; at least one, second, moveable member that is mounted on the rotatable shaft adjacent to the first member, that rotates with the rotatable shaft, and that is electrically conductive to the exciting current and that defines, with the first member, an annular volume between the first and second members; and third, relatively moveable members that are electrically conductive to the exciting current, that are disposed between the first and second members in the annular volume, that have an electrically conductive grease which is packed in the annular volume and about the third members, and that permits the second member to rotate, relative to the first member, with relatively minimal friction between the first, second and third members.
These objects are met, in whole or in part, by an improved alternator of the present invention which may employ a rotor assembly, a stator assembly and a rotor shaft like those used in brush-type alternators but which does not utilize conventional brushes for supplying exciting current to the rotor assembly. More specifically, improved alternators of the present invention comprise a rotor assembly and a stator assembly, both of which assemblies may be of conventional design, and an improved contact assembly, which is used to supply exciting current to the rotor assembly instead of the conventional brush structures previously employed in brushtype alternators. In the preferred embodiments, the contact assembly includes two relatively low friction ball bearing assemblies that are electrically isolated from each other and that have components made of an electrically conductive materials. Each of the ball bearing assemblies has an outer race that is electrically connected to an inner race. This electrical connection between each bearing assembly""s respective inner and outer races is provided by a plurality of bearing balls disposed between the inner and outer races, and additionally, by a highly electrically conductive grease that is packed about the balls and between the spaces around the balls so that the balls and grease substantially fill the annular volume defined between the inner and outer races. The inner races of the ball bearings are mounted on and rotate with the rotor assembly shaft. The ball bearings"" outer races are held relatively stationary with respect to the inner races and are connected with field conductors, which, in turn, are connected with a source of DC exciting current such as, for example, a conventional storage battery. The contact assembly of the present invention may also be enclosed in a cartridge housing that is made of an electrical insulative material and that maintains the outer races of the bearing assemblies axially aligned with and concentric about the longitudinal axis of the rotor shaft. The rotor shaft, adjacent to the contact assembly, includes stepped diameter portions that facilitate the assembly of the bearing assemblies into and about the rotor shaft.
The improved alternator of the present invention affords commercially important advantages vis-a-vis conventional brush-type and brushless-type alternators. The improved alternator eliminates brushes, and their concomitant problems, and gives the long life characteristics of a brushless-type alternator. The improved alternator also provides the output characteristics of a brush-type alternator, which includes good output at low rpms as, for example, at 5000 rpms. The improved alternator also requires less space than conventional brushless-type alternators with the same output and is more economical and lighter in weight.
Certain embodiments of the present invention provide an improved alternator for use with motor vehicles and for supplying AC current for the operation of the motor vehicle in response to a DC exciting current being supplied to the alternator from a source of exciting current. The improved alternator comprises a rotor shaft and a contact assembly. The rotor shaft has first and second ends and an axis of rotation. The contact assembly comprises first and second bearing assemblies and at least one spring member. The contact assembly comprises first and second bearing assemblies that are disposed adjacent to the first end of the rotor shaft. The first and second bearing assemblies are coaxially aligned with the rotor shaft. The first and second bearing assemblies are longitudinally spaced from one another by a first spacer. The bearing assemblies are electrically isolated from one another. Each of the first and second bearing assemblies have an outer race member that is relatively fixed with respect to the rotor shaft.
The first spring member is coaxially positioned with respect to the rotor shaft within the contact assembly. The first spring member exerts at least one resistive force into at least one of the first and second bearing assemblies in order to maintain a constant axial force between the first and second bearing assemblies. The improved alternator may also comprise a second spring member. The spring member(s) exerts resistive forces into at least one of the first and second bearing assemblies and support structures within said chamber in order to compressively sandwich the first and second bearing assemblies within the chamber of the contact assembly.
Additionally, the improved alternator may also comprise a locating sleeve positioned over the bearing assemblies. The locating sleeve ensures and maintains proper axial alignment of the rotor shaft and the bearing assemblies.
The bearing assemblies may be retained, in part, by bearing holders. Each bearing assembly is retained by a separate bearing holder. The bearing holders are separate and distinct from one another in order to allow relative motion between the first and second bearing holders.
The improved alternator of may also comprise at least one capacitor in electrical communication with each of said first and second bearing assemblies. The capacitor(s) absorb electrical charges produced by arcing, sparking and the like.
Certain embodiments of the present invention also provide a method of manufacturing a contact assembly of an alternator. The method comprises the steps of positioning a rotor shaft having an axis of rotation within an interior chamber of the contact assembly; coaxially positioning a slip ring over the rotor shaft; coaxially positioning two bearing assemblies over the slip ring and the rotor shaft; mechanically and electrically isolating the two bearing assemblies from one another; and compressively sandwiching the two bearing assemblies together along the axis of rotation by way of at least one spring member. The method may further comprises the step of ensuring proper axial alignment of the rotor shaft and the bearing assemblies through a locating sleeve positioned over the bearing assemblies. Additionally, the method may comprise the step of retaining each of the two bearing assemblies through separate and distinct bearing holders, each of the bearing holders moving independent of the other. Also, the method may comprise the step of electrically connecting at least one capacitor to the two bearing assemblies.